(adapted from project decription)
Problems: Tillage practices impact the movement of sediment within
and from watersheds. How do conservation tillage practices influence
the movement of carbon attached to the sediments -- both loss and
deposition within a watershed as well as the amount moved from a small
watershed?
Approach: In small watersheds instrumented with H-flumes and Coshocton
wheels, flume floor sediments and sediment in runoff have been
collected from several conservation tillage practices (no-till,
chisel-plow, paraplow, disk) for 11 years. Samples of sediment
deposited within watersheds following a runoff event have also been
collected.
Findings: Our work with carbon storage research is recent, and the
results are still only preliminary. Although the weighted averages of
total soil carbon may not be significantly different for the sediment
from the different tillage treatments, carbon content of no-till
sediments was greatest (2.8%) and chisel-plow was lowest
(1.9%). Annual total carbon transport (the product of total sediment
transport times the carbon content) was similar for these two
practices; 11.9 and 12.1 kg/ha, respectively. Annual average carbon
transport from the disk treatment was 17.1 kg/ha. Although tillage
treatments may reduce carbon transport in sediment by lower content, a
greater factor for reducing carbon movement is by reducing sediment
transport.
With soil samples from two conservation tillage watersheds (no-till
and chisel-plow) following summer thunderstorms, characterization of
soil deposited in rills and inter-rill areas and the sediment carried
in runoff waters was contrasted with the near-surface topsoil. The two
watersheds showed similar trends. Suspended sediments from large
events had higher C and slightly lower C/N ratio than flume floor
samples. The C/N ratios of soil samples (0-1 and 0-5 cm depth) and
landscape deposits (averaging between 14 and 22) were higher than the
C/N ratios of fiume deposits and runoff sediments (averaging 8 to 11
).
Future Plans: We have stored soil and sediment samples for nearly 12
years from conservation tillage watersheds. These will be analyzed for
total C (some C fractionation will be done, if adequate resources are
available). Carbon content changes overtime will be studied and
contrasts with C content of sediments will be made to validate
preliminary findings. The study of carbon content and transport on
sediments within a watershed will be expanded to other watersheds and
conservation tillage practices. Understanding transport mechanisms may
lead to development of conceptional models for predicting C dynamics
in agriculture.